P22 - Competitive advantages

The theoretical background to the thermodynamic method is primarily in the public domain, being documented in ISO and other standards. The performance of an instrument employing this method is largely determined by the design, accuracy and stability of the temperature and pressure probes.

P22 design overview

Pump efficiency is measured by accurate and innovative temperature and pressure probes. The electronic circuits are contained in the probe handles, thus eliminating potential errors from connector and cable resistances. The design allows the self-contained calibration of each temperature and pressure probe, without reference to any external electronic components. This greatly simplifies operational use and maintenance, and also facilitates measurements on multiple combinations of pumps.

The probes are connected to each other and to the control computer by an RS485 serial interface (Modbus™ protocol), which provides high immunity to electromagnetic interference over long distances. The connecting cables only carry the digital signals and the power to the probes.

This concept allows probes to be connected in series, so that one computer can simultaneously monitor banks of pumps, connected either in series or parallel. Up to 128 probes can be connected to one RS485 interface. Similarly, several temperature probes can be connected in series for averaging fluid temperature in very large pumps or turbines. The temperature probes employ a novel design to ensure high sensitivity and long-term stability. The pressure probes are accurate over a very wide range, so that one set of probes can cover most applications.

It is desirable to measure the differential temperature across the pump to an accuracy of 1 mK or better. This is one particular area where we have made a number of significant technological advances with the P22's temperature probes.

The use of industry standard RS485 communications allows integration with vibration and bearing temperature measurement for complete condition monitoring.

Temperature Probes

Sensitive, accurate and stable for both fixed and portable operation:

• each temperature probe has dual sensors, to detect drift in an individual sensor. The sensors and signal conditioning electronics are stable over long time periods. Experience over several years shows no observable drift (less than 0.25 mK)
• The sensors give a high electrical signal, which minimises electronic noise. With the standard temperature probes (0 - 45°C), the precision of each temperature point (1 standard deviation) due to electronic noise is 0.11 mK. A set of 25 readings results in a standard error of 0.025 mK for the average temperature. The standard error in the average differential temperature due to electronic noise will then be 0.035 mK.
• The signal conditioning electronics minimises self-heating effects in the sensors.
• The probes are designed to minimise stem effects, which can otherwise occur due to differences between the fluid and ambient temperatures.
• Correction is made for viscous heating effects.

Pressure Probes

The pressure probes have in-built temperature sensors and active temperature correction. The accuracy of 0.1% is maintained over a wide temperature range, not just at one temperature.

The probes are accurate over a wide pressure range, so that one set of probes can cover most applications.

Power Meter

Accuracy of flow measurement depends on the accuracy of the power meter and the efficiency measurement:

• the P6000 power meter is auto-ranging and has accuracy for kW of 0.25% of full scale.

Ease of Operation

• Since the temperature probes are very stable over long periods of time, it is not necessary to swap over the temperature probes and average two measurements.
• Probes can readily be disconnected from their cables, for ease of transport, storage, calibration, and maintenance.
• The main data acquisition screen gives averages, maxima, minima, and standard deviations of key parameters, to assist the operator in checking the stability of the pump operating point.
• The control and analysis software program is easily upgradeable, on the control computer. Much easier to upgrade than firmware. Just receive a new exe file by email and replace using Windows Explorer.
• Wireless connections between the probes, power meter, and computer are standard for the portable unit, as is battery operation of probes. This reduces cabling to a minimum, providing a lightweight unit and greatly facilitating operation and storage.

Case Studies

Accurate comparisons have been made with flow rates measured volumetrically by level sensors in large tanks, and agreement is within 1%.